LED Load Control With Multi-Mode Burst Dimming
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Solution Overview
Problem
Traditional dimming methods for LED light sources result in perceptible changes in light intensity, particularly at low intensity levels, necessitating improved dimming techniques for smoother intensity adjustments.
Innovation Solution
A load control device and LED driver utilizing a burst duty cycle mechanism to adjust the active and inactive states of an inverter circuit, allowing for fine control of load current and intensity, especially at low intensity ranges, through a control circuit that operates in low-end, intermediate, and normal modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If traditional dimming methods (PWM or CCR) are used to reduce LED intensity, then energy consumption is reduced, but perceptible changes in light intensity occur especially at low intensity levels
Solution Approach 1:
The patent applies periodic action by using pulse-width modulation (PWM) to switch the LED on and off at high frequency. By controlling the duty cycle of these periodic pulses, the average light output is reduced while maintaining the LED at full intensity during active periods, thereby avoiding perceptible dimming steps and achieving smooth intensity reduction with lower energy consumption.
2Illumination intensity
If PWM dimming is used with varying duty cycle, then average current and light intensity are reduced, but perceptible steps in intensity changes occur
Solution Approach 1:
The patent changes the parameter of switching frequency in addition to duty cycle. By dynamically adjusting both the duty cycle and switching frequency of the PWM signal, the system achieves finer control resolution and smoother intensity transitions. The frequency adjustment allows optimization of the PWM period to match human visual perception thresholds, eliminating perceptible steps in intensity changes.
3Illumination intensity
If CCR dimming is used to reduce DC current magnitude, then light intensity is reduced, but perceptible changes occur particularly at low intensity ranges
Solution Approach 1:
The patent replaces the direct current magnitude control mechanism with a pulsed control mechanism. Instead of continuously varying the DC current magnitude (CCR), the system uses high-frequency PWM to switch current on and off, controlling average intensity through duty cycle. This substitution provides higher control precision because the LED operates at full current during active periods, maintaining optimal light output characteristics while achieving precise intensity control through temporal modulation.
Data Source
AI summary
A load control device for regulating an average magnitude of a load current conducted through an electrical load may operate in different modes. The load control device may comprise a control circuit configured to activate an inverter circuit during an active state period and deactivate the inverter circuit during an inactive state period. In one mode, the control circuit may adjust the average magnitude of the load current by adjusting the inactive state period while keeping the active state period constant. In another mode, the control circuit may adjust the average magnitude of the load current by adjusting the active state period while keeping the inactive state period constant. In yet another mode, the control circuit may keep a duty cycle of the inverter circuit constant and regulate the average magnitude of the load current by adjusting a target load current conducted through the electrical load.